1. Field of the Invention
This invention generally relates to electron injectors, and more particularly to injectors that inject electrons in multiple directions into an evacuated passageway of a Betatron.
2. Background of the Invention
A Betatron is an electron accelerator that produces a high energy electron beam. If this beam is directed on a suitable target high energy x-rays are produced. Thus, the Betatron serves as a source of high energy x-rays. It operates by appropriately pulsing a magnetic field around an evacuated toroidal passageway having an interior volume that is periodically filled with electrons. The electrons are injected from the inner or outer diameter of the volume with some critical energy and are subsequently trapped into orbits dictated by the applied magnetic field and accelerated by the electromotive force (EMF) induced by the rapidly rising magnetic field.
Electron injection is typically timed to occur at the beginning of every acceleration cycle and aimed to accelerate electrons in one angular rotational direction. In some implementations of the Betatron the magnetic field is increased from a zero value to its maximum value and then returned to zero and this is repeated cyclically. In other applications the magnetic field is made to vary between a maximum positive and an equal opposite negative value. This affords to opportunities for injection during one full cycle. However, the second cycle having the opposite magnetic field the injection needs to be in the opposite direction. A standard injector is only capable of injecting in one direction, thus neglecting the opposite accelerating field that would be available in the second half cycle. Acceleration in alternate directions has been disclosed in Betatrons in the past, for example U.S. Pat. No. 4,577,156 to Kerst discloses two Betatron tubes, one above the other. Each tube has a separate electron injector and separate target. A first injector injects a beam of electrons into the first tube in a first direction when an accelerating flux is changing from its positive maximum to its negative maximum. The second injector then injects a beam of electrons into the second tube in an opposing second direction when the accelerating flux is changing from its negative maximum to its positive maximum. A single tube embodiment having two spaced apart injectors is also disclosed. U.S. Pat. No. 4,577,156 is incorporated by reference in its entirety herein.
There remains, a need for a single compact injector for a more efficient, compact, reliable and manufacturable system.